Reconstructing the oceanic p13sSeuss effect
This dissertation consists of two components: deriving along-isopycnal advection rates in the North Pacific from chlorofluorocarbon (CFC) distributions and determining 13C/12C changes in the global ocean due to oceanic uptake of anthropogenic CO2.Thermocline ventilation rates for the subtropical North Pacific were determined using a 1-dimensional (meridional) along-isopycnal model tuned to (CFC) concentrations measured along 152°W in 1991. Mean southward advection rates in the subtropics ranged from 1.0 to 0.6 cms-1 between sq=25.5 and 26.6, and ventilation times for the subtropical gyre increased from about 10 to 27 years over that isopycnal range. Oxygen utilization rates (OURs) determined with the model decreased from 6.6 to 3.2 gmol kg -1 yr-1 between sq=25.5 and 26.6. Extrapolation of the OUR versus depth trend to the base of the euphotic zone and integration from 500 to 100 meters depth implied a carbon export rate of 2.2 +/- 0.5 moles C M-2 yr -1 from overlying surface waters at 30°N, 152°W.The rate of anthropogenic delta13C change in the oceans during 1968 to 1991 was determined from trends in preformed 13C/ 12C of dissolved inorganic carbon (DIC) and CFC-derived water ages on isopycnal surfaces, and, in the Indian Ocean, using a multiparameter linear regression (MLR) comparison of 1978 GEOSECS and 1995 WOCE delta13 C of DIC, hydrographic and nutrient data. The change rate of delta 13C in the surface ocean increased from about --0.13 ‰ decade-1 in the tropics to approximately --0.2 ‰ decade-1 within the subtropics, and then decreased to around --0.196 ‰ decade-1 in the subpolar oceans. Our reconstructions implied ocean-wide average surface ocean and depth integrated delta 13C change rates of --0.15 to --0.17 ‰ decade -1 and --7.9 +/- 3.1 mumol kg-1 yr -1, respectively, using extrapolations based on ocean model predictions (Bacastow et al., 1996) and correlations with GEOSECS bomb 14C inventories, respectively. The integrated delta13C change implied global ocean CO2 uptake rates during 1970--1990 of 1.3 +/- 1 Gt. C yr-1 and 2.0 +/- 0.9 Gt. C yr -1 using the 13CO2 and 12CO 2 budget of Quay et al. (1992) and dynamic constraint method of Heimann and Maier Reimer (1996), respectively.
- Oceanography